Various types of carbon black that differ in properties have been used for rubber reinforcement applications. Since the properties of the carbon black are major factors that determine the performance of the resulting rubber, carbon black having properties suitable for the target application is selected, and added to a rubber composition.
For example, high-structure hard carbon black having a small particle size and a large specific surface area (e.g., SAF (N110) or ISAF (N220)) has been used for a rubber member (e.g., tire tread) for which high abrasion resistance is required. However, a rubber obtained using a rubber composition that includes carbon black is highly reinforced, and exhibits high abrasion resistance, but tends to exhibit high heat buildup and low impact resilience.
In recent years, development of fuel-efficient tires has been increasingly desired in order to address a social need for saving resources and energy, and a rubber composition that achieves low heat buildup and high resilience suitable for fuel-efficient tires has been extensively developed. Low heat buildup and high resilience have been normally achieved by adding carbon black having a large particle size and a small specific surface area to a rubber composition.
A rubber that is highly reinforced, and exhibits excellent abrasion resistance, low heat buildup, and high resilience is required to produce the tread of fuel-efficient tires. However, since carbon black that is used to improve the degree of reinforcement and abrasion resistance and carbon black that is used to improve heat buildup and resilience completely differ in particle size and specific surface area and have a trade-off relationship, it is difficult to obtain the desired rubber composition by adjusting the particle size and the specific surface area of the carbon black.
In order to deal with the above problem, technology has been proposed that improves rubber properties (e.g., degree of reinforcement, abrasion resistance, heat generation property, and impact resilience) by microscopically evaluating the colloidal properties of carbon black in addition to the particle size, specific surface area, structure, and the like (that have been regarded as important as the basic properties of carbon black used for rubber reinforcement applications), and adding carbon black that has specific properties to a rubber component (see Patent Document 1 (W-A-2002-188022) and Patent Document 2 (JP-A-8-169983), for example).